@disneymagicgirl You'd definitely have to price it out carefully and weigh it against your family's priorities and reasonable expectations of how much of the parks you'll actually get through. Though EP is a big upgrade if not included at the hotel, it might still work out cheaper when you're weighing it against a family suite ($160-180 range) at Cabana Bay versus two rooms at one of the deluxe hotels. I'm not sure. You'd have to check that time of year and the room costs. And the thought was more if it's a low-crowd day and/or you're taking longer in one of the parks than you thought (hence not actually getting to enjoy both in a worthwhile way), it might end of being a major saving to wait and just do the upgrades in parks.
My family was at Universal for the first time last year at the same time of year as you're going. We had significantly longer than a day to enjoy the parks and were staying on-site. But it was definitely a low-crowd period and I don't feel we would've needed the EP. And we are crowd and line adverse as well. The longest two lines we waited in were MIB and Kong. They were both maybe a 10-15 minute wait. Even FJ and Gringott's, even though they were listed as a 20 minute wait time, it was just walking through the queues and then standing for all of one or two loads in front of us when we got up to the ride vehicles. The queues are so themed at Universal you almost want to have a bit of a wait time to see them. In the FJ (Hogwart's castle) we actually stepped to the side and let people go by us so we could stand and watch some of the animations and interactions and look at the themeing. We saw several rides listed as a 0 or 5 minute wait time while we were in the parks.
I'm not sure how many days a regular ticket is good for. I suspect it is 7 or 10. The tickets we had, which were in a hotel package, were good for 14, though. You'll have to check the small print. Though, you might again want to look at
UT as I've seen lots of people posting that right now they have a 2 Day ticket that adds 2 Days free and then they've taken that to guest services while they're at Universal and had it upgraded to a seasonal pass for free (or a nominal fee or sometimes even a small refund in a few cases it sounds like). You'd have to check the details to see what the different levels include and if that might make it a better cost-saving options too. I do know that APs give you room discounts (which apparently you don't need to have the AP pass yet when you book and just need to show it to the front desk before you check out to maintain the rate), which might be useful to you if booking two rooms. And some also include EP after 4 p.m. and some kind of parking discount.
We definitely aren't a command and conquer family. At Disney or otherwise. And we had a lot more time to go through US/IoA at our leisure. But I have trouble seeing how to get through both parks in a way that would really make full use of a 2P ticket in one day. Though, I absolutely get the desire to do so. I'm also not sure that I'd honestly say that say if your kids are mostly interested in the IoA area, if paying the P2P upgrade when you might just have time to see Diagon Alley is worth it (and we definitely liked Diagon Alley side better ... but I'm just not sure a couple hours on the US side would be worth the cost, especially if you think you are likely to be back to US another time and it's not a one-time thing).
To give you an idea of what our family (which has a variety of age ranges and a medical issue that means our days are shorter) did in a day:
One Day we did: US. Did not do EE but arrived early in the day. Did the Shrek show. Did Transformers meet-and-greet. Wandered San Fransisco Area (Jaws display), went into Diagon Alley and did the shops, had a butter beer, rode Gringott's twice, watched the dragon breath fire, bought a wand, did MIB, ate some lunch, stopped and watched the street drummers show, did the Horror Make-Up show. And then went back to the hotel in mid-afternoon.
Two Day we did: IoA. Did not do EE but arrived early in the day. Looked around Seuessland. Rode Cat in the Hat. Explored Hogsmead and did all the wand stations. Did the wand show. Rode FJ and Flight of the Hippogriff. Walked through to Jurassic Park. Spent some time in the Discovery Center. Had lunch. Rode Kong. Watched the super heroes do their drive-by. Rode Spiderman (this was a 0 minute wait). And then we headed out. Again this was about 2-ish in the afternoon.
Three Day we did: EE through the IoA gate. Explored Hogsmead again and redid some of the wand spots and went into some of the shops in low crowds. Took the train over to Diagon Alley. Did all the wand spots there. Rode Gringotts again. Took the train back to Hogsmead. Went back into Seussland. Looked in some shops. Rode the trolley. Watched Grinchmas. Looked in some more shops (including a Christmas store) on the way out. So again, about half a day.
Four Day we did: Went over in the mid-afternoon. Saw the end of the parade. Rode ET. Think it was a Trolls meet and greet there. Got some snacks. Snagged a spot for the Macy's parade. Watched the parade. We had intended to then take the train over to Hogsmead again to watch the night show projections on Hogswart. Unfortunately everyone else had that same idea and this was the only time we wished we had an EP. I forget how long the wait was but it was ridiculous and we dropped that idea. Instead we backtracked. Looked at the large Christmas tree lit up. Rode the Mummy. There was a minor wait time for JFNY but we decided to forego that when we walked passed. We watched a bit of MS and then we exited. We thought about trying to walk over to IoA and up to HP to see the projection. But it is quite the walk and it was getting close to closing time. So we decided to just call it quits.
We honestly felt like we just scratched the surface in the time we had. We can't command and conquer given our family's limitations. But I still feel that it'd be hard even for an able-bodied, age-appropriate family to really do it all in one day in an enjoyable way. Even with EP. I know some people will absolutely disagree and will have done it.
I will say that the parks (due to the water features in the middle of them) are a lot bigger with a lot more walking than they look on the map and there's not many short-cuts. You kind of have to walk the whole circuit one way or the other to get to what you want in most cases. And also there really is some beautiful theming done in the parks and if you power through to just hop on and off the rides, you'll likely miss a lot of that and the visual gags and winks in the parks.
We were impressed with them enough we've decided to go back to get more done as there were several things we were disappointed we didn't have time for. I don't feel EP would've helped us get on more since lines and crowds really weren't an issue for us beyond that one night (which was a Saturday). It was really just our limitations and the way we travel.
So I'd say that if you get EP or not is sort of a gamble on what crowds are like that particular day. And then it all really boils down to what your family's priorities are in terms of tours and attractions, how they approach touring parks, and what you can afford. If your budget lets you do two rooms at a deluxe or accommodates upgrading to an EP -- then it's probably just a matter of what kind of gambler you are and if you'd rather be safe than sorry.
Also make sure you check the park times that day. US/IoA definitely aren't open as late as the Disney Parks either. They were closing around 6/7 most nights we were there last year. With it being a Friday, it might be 8 or 9 but you should definitely check. Because it does mean you have less time in a day to get through both parks. Likely only about 12 hours -- maybe closer to 14 if you're lucky.
Good luck with your planning. I hope your family enjoys your first time in US as much as we did.